In X-ray based medical imaging a patient is exposed to a radiation risk. It is imperative to minimize this risk without constraints being imposed on the medically necessary requirements.
C-arm systems are used very frequently for medical diagnostics and in the present case said systems are to serve as an example of X-ray apparatuses which can be adjusted to different angular positions during the image acquisition. Systems of this kind are characterized in that radiation can be passed through the patient in any direction without the patient having to be repositioned. This is of great advantage in particular in angiography, since vessels can be assessed and treated better when they can be examined from different sides.
In X-ray diagnostic systems there is generally not only the stochastic radiation risk but also in addition a deterministic risk which denotes the danger that the skin on the radiation input side will be burned if the dose is too high. With regard to the deterministic risks, in contrast to the stochastic risk, it is possible in most cases to specify dose limit values below which deterministic radiation damage can be almost totally ruled out. For this reason physicians will usually proceed in such a way that during a diagnosis or, as the case may be, a treatment they will change the angulation, i.e. the angular position, of the X-ray apparatus every once in a while for radiation protection reasons in order to distribute the entry radiation exposure over a greater area of the body. In order to support the physicians in this endeavor programs have been developed which determine the surface dose on a location-dependent basis with the aid of models and report said dose back to the physician. In this case the patient surface currently being irradiated is determined from the angular position of the X-ray apparatus and the so-called collimation, i.e. the area or, as the case may be, field which is radiated onto the patient by the X-ray source. The doses that have accrued on said areas over a specific time period are subsequently aggregated and displayed or visualized on a display. Since the treating or diagnosing physician is occupied with numerous medical tasks, it represents an additional onerous task for him/her if he/she then also has to rotate the model with the dose displayed thereon so that the angular position of the model corresponds to the angular position of the X-ray apparatus.
U.S. Pat. No. 7,103,139 B2 discloses a method according to the preamble of claim 1 for displaying the dose of X-ray radiation applied to a surface of a patient in a defined time period by means of an X-ray apparatus which can be set to different angular positions.